(1) Field of the Invention
The present invention relates to a detecting device provided for detecting the state of a moving object being conveyed.
(2) Description of the Prior Art
In an image forming apparatus, a sheet-like material such as plain paper etc. is fed into the image forming position. For this operation, in order to synchronize the timing of delivering the sheet to the image forming position with the entrance of the image forming area into the image forming position, detecting devices for detecting the presence of the sheet are provided in the sheet conveying system.
A plurality of detecting devices are disposed in the above sheet conveying system. In response to the detection of the sheet by the detecting devices, the image forming and other operations are controlled while the conveyed state of the sheet in the conveying system can be detected. Therefore, it is possible to easily detect a delay in the conveyance of the sheet in the conveying system as well as sheet jam and other deficiencies, due to a conveying failure.
An example of the detecting device is constructed, as shown in FIG. 1, such that an actuator 50 having a front end placed in the sheet conveying path is pivotally supported by a rotary shaft 51 so as to be swayed or pivoted by a conveyed sheet while a slit arm 52 provided in the lower part of actuator 50 is interposed between the light emitting and receiving elements of an optical sensor 53. Slit arm 52 is integrally formed of resin with actuator 50, and is provided with a slit 52a which is of a square shape recess from the bottom thereof. A light-blocking part 52b other than slit 52a stays in the optical path of the optical sensor 53 to block the light.
In this arrangement, a sheet move the front end of actuator 50 so as to pivot actuator 50 about rotary shaft 51. This causes slit arm 52 at the bottom to rotate (or move) so that slit 52a reaches the optical path of optical sensor 53 and hence a light-reception signal is outputted. Therefore, when a sheet arrives at actuator 50, the conveyance of the sheet to that position can be detected.
Optical sensor 53 typically comprises a photo-interrupter which has light emitting and receiving elements embedded in the base part formed in a U-shape. Placed between these elements is the aforementioned slit arm 51 integrated with actuator 50. Slit arm 51 has an urging portion 55 which serves as a weight for restoring the original state after the passing of a sheet and rotationally urges actuator 50 generally in the clockwise direction shown in FIG. 1. This urging portion 55 is adapted to abut the base of optical sensor 52 to thereby constrain the rotational movement of actuator 50 and position it at a state allowing detection of a sheet to be conveyed.
Illustratively, actuator 50 when it reverts back to the original position, should be positioned exactly at the original position. For this purpose, urging portion 55 also is provided with an abutment surface, while in optical sensor 53 the unit base is configured as the positioning member therefor.
In the detecting device shown in FIG. 1, a very light actuator 50 which can sway by a slight action force when a sheet passes therethrough is used so that it can reliably operate in accordance with the passing of a sheet. It is important that actuator 50 and optical sensor 53 operate without contact with each other and actuator 50 is formed so as to be light-weighted as stated above.
However, urging portion 55 integrally formed with actuator 50 in stand-by state is at such a position as to abut the unit base of optical sensor 53, and is pivoted by the passage of a sheet, and reverts to the original stand-by position in response to the passage of the rear end of the sheet. At this moment when the abutment surface for positioning urging portion 55 instantly collides against the unit base as a positioning member of optical sensor 53, the urging portion receives a repulsive force O shown in FIG. 1 so that actuator 50 bounces in that direction. As a result, slit 52a of slit arm 52 allows the optical path of optical sensor 53 to open. Therefore, despite of no sheet passage, a light-receiving signal is outputted as if there was a sheet passage. This phenomenon is generally called `chattering`.
Conventionally, some electrical methods have been proposed to solve the problem of chattering. One of the ideas is to delay detection during the generation of chattering.
However, such an electrical method of solving the problem of chattering will also delay the timing of actual detection. Further, extra circuit configurations are required for causing the delay, resulting in significant disadvantage in cost.